Decrement the reference count for object o. The object must not be NULL; if
you aren’t sure that it isn’t NULL, use Py_XDECREF(). If the reference
count reaches zero, the object’s type’s deallocation function (which must not be
NULL) is invoked.

Warning

The deallocation function can cause arbitrary Python code to be invoked (e.g.
when a class instance with a __del__() method is deallocated). While
exceptions in such code are not propagated, the executed code has free access to
all Python global variables. This means that any object that is reachable from
a global variable should be in a consistent state before Py_DECREF() is
invoked. For example, code to delete an object from a list should copy a
reference to the deleted object in a temporary variable, update the list data
structure, and then call Py_DECREF() for the temporary variable.

Decrement the reference count for object o. The object may be NULL, in
which case the macro has no effect; otherwise the effect is the same as for
Py_DECREF(), except that the argument is also set to NULL. The warning
for Py_DECREF() does not apply with respect to the object passed because
the macro carefully uses a temporary variable and sets the argument to NULL
before decrementing its reference count.

It is a good idea to use this macro whenever decrementing the value of a
variable that might be traversed during garbage collection.

The following functions are for runtime dynamic embedding of Python:
Py_IncRef(PyObject*o), Py_DecRef(PyObject*o). They are
simply exported function versions of Py_XINCREF() and
Py_XDECREF(), respectively.

The following functions or macros are only for use within the interpreter core:
_Py_Dealloc(), _Py_ForgetReference(), _Py_NewReference(),
as well as the global variable _Py_RefTotal.